Present developments in wireless technology may adapt broadcasting to mobility services. One limitation has been that broadcasting may often require high bit rate data transmission at rates higher than could be supported by existing mobile communications networks. However, with emerging developments in wireless communications technology, even this obstacle may be overcome. Terrestrial television and radio broadcast networks have made use of high power transmitters covering broad service areas, which enable one-way distribution of content to user equipment such as televisions and radios. By contrast, wireless telecommunications networks have made use of low power transmitters, which have covered relatively small areas known as “cells”. Unlike broadcast networks, wireless networks may be adapted to provide two-way interactive services between users of user equipment such as telephones and computer equipment.
Standards for digital television terrestrial broadcasting (DTTB) have evolved around the world with different systems being adopted in different regions. The three leading DTTB systems are, the advanced standards technical committee (ATSC) system, the digital video broadcast terrestrial (DVB-T) system, and the integrated service digital broadcasting terrestrial (ISDB-T) system. The ATSC system has largely been adopted in North America, South America, Taiwan, and South Korea. This system adapts trellis coding and 8-level vestigial sideband (8-VSB) modulation. The DVB-T system has largely been adopted in Europe, the Middle East, Australia, as well as parts of Africa and parts of Asia. The DVB-T system adapts coded orthogonal frequency division multiplexing (COFDM). The ISDB-T system has been adopted in Japan and adapts bandwidth segmented transmission orthogonal frequency division multiplexing (BST-OFDM). The various DTTB systems may differ in important aspects; some systems employ a 6 MHz channel separation, while others may employ 7 MHz or 8 MHz channel separations.
Even among countries adopting a common DTTB system, variations may exist in parameters adapted in a specific national implementation. For example, DVB-T not only supports a plurality of modulation schemes, comprising quadrature phase shift keying (QPSK), 16-QAM, and 64 level QAM (64-QAM), but DVB-T offers a plurality of choices for the number of modulation carriers to be used in the COFDM scheme. The “2K” mode permits 1,705 carrier frequencies that may carry symbols, each with a useful duration of 224 μs for an 8 MHz channel. In the “8K” mode there are 6,817 carrier frequencies, each with useful symbol duration of 896 μs for an 8 MHz channel. In SFN implementations, the 2K mode may provide comparatively higher data rates but smaller geographical coverage areas than may be the case with the 8K mode. Different countries adopting the same system may also employ different channel separation schemes.
While 3G systems are evolving to provide integrated voice, multimedia, and data services to mobile user equipment, there may be compelling reasons for adapting DTTB systems for this purpose. One of the more notable reasons may be the high data rates that may be supported in DTTB systems. For example, DVB-T may support data rates of 15 Mbits/s in an 8 MHz channel in a wide area SFN. There are also significant challenges in deploying broadcast services to mobile user equipment. Many handheld portable devices, for example, may require that services consume minimum power to extend battery life to a level, which may be acceptable to users. Another consideration is the Doppler effect in moving user equipment, which may cause inter-symbol interference in received signals. Among the three major DTTB systems, ISDB-T was originally designed to support broadcast services to mobile user equipment. While DVB-T may not have been originally designed to support mobility broadcast services, a number of adaptations have been made to provide support for mobile broadcast capability. The adaptation of DVB-T to mobile broadcasting is commonly known as DVB handheld (DVB-H).
To meet requirements for mobile broadcasting the DVB-H specification may support time slicing to reduce power consumption at the user equipment, addition of a 4K mode to enable network operators to make tradeoffs between the advantages of the 2K mode and those of the 8K mode, and an additional level of forward error correction on multi-protocol encapsulated data—forward error correction (MPE-FEC) to make DVB-H transmissions more robust to the challenges presented by mobile reception of signals and to potential limitations in antenna designs for handheld user equipment. DVB-H may also use the DVB-T modulation schemes, like QPSK and 16-quadrature amplitude modulation (16-QAM), which may be more resilient to transmission errors. MPEG audio and video services may be more resilient to error than data, thus additional forward error correction may not be required to meet DTTB service objectives.
The MPE-FEC may comprise Reed-Solomon coding of IP data packets, or packets using other data protocols. The 4K mode in DVB-H may utilize 3,409 carriers, each with a useful duration of 448 μs for an 8 MHz channel. The 4K mode may enable network operators to realize greater flexibility in network design at minimum additional cost. Importantly, DVB-T and DVB-H may coexist in the same geographical area. Transmission parameter signaling (TPS) bits that are carried in the header of transmitted messages may indicate whether a given DVB transmission is DVB-T or DVB-H, in addition to indicating whether DVB-H specific features, such as time slicing, or MPE-FEC are to be performed at the receiver. As time slicing may be a mandatory feature of DVB-H, an indication of time slicing in the TPS may indicate that the received information is from a DVB-H service.
Time slicing, as used by DVB-H, may reduce power consumption in user equipment by increasing the burstiness of data transmission. Instead of transmitting data at the received rate, under time slicing techniques, the transmitter may delay the sending of data to user equipment and send data later but at a higher bit rate. This may reduce total data transmission time over the air, time, which may be used to temporarily power down the receiver at the user equipment. Time slicing may also facilitate service handovers as user equipment moves from one cell to another because the delay time imposed by time slicing may be used to monitor transmitters in neighboring cells. The increased burstiness of DVB-H data transmissions, however, may result in an increase of the processing data error rate since the DVB-H receiver has to process the received DVB-H packets in a substantially reduced time.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.